Conventionally, in the image formation method which forms a visible image by an electrophotographic method, a heat fixing method has been widely used. In this fixing method, heat is used to fix a toner image as a way to fix an image formed on an image supporting material such as paper. In order to secure the fixability in this heat fixing method, i.e., to secure the adhesion property of the toner to the image supporting material, it is required a high amount of heat to some extent.
However, originated from the request of the warming preventive measures for the global environment in recent years, it is also demanded energy saving in the electrophotographic image formation apparatus which adopts the heat fixing method. In order to respond such request, it has been examined the way to reduce the heat needed for image fixation of the toner by using a toner which can fix the image at a low temperature, namely, by using a toner having a property of so called low-temperature fixability. And in order to acquire a tone of low-temperature fixability, it is widely known that a resin having a high sharp-melting nature is an effective approach as a composing element of a toner. A polyester resin is useful as a resin which has such characteristics.
On the other hand, various kinds of toners were proposed in which a polyester resin was contained as a composition of the toner (for example, refer to Patent document 1 and Patent document 2). In order to respond the request of achieving much lower temperature fixability of the visible image demanded in connection with the expanding use of image formation method by an electrophotographic method for various fields, improvement in further low-temperature fixability was intended by setting up the molecular weight to be low, for example.
However, in the toner containing a polyester resin of low molecular weight described in Patent document 1 and Patent document 2, there are problems of generating photoreceptor filming caused by mechanically weak polyester resin and carrier staining when used in a two-component developer as a developer.
Patent document 1: Japanese Patent Application Publication (JP-A) No. 2009-210723
Patent document 2: JP-A No. 2009-200225